This invention relates generally to a system and method for monitoring and controlling nitrogen pumping at an oil or gas well.
Numerous operations are performed on oil and gas wells which require large volumes of nitrogen gas. These operations may be performed on both onshore and offshore wells. Several examples are listed in U.S. Pat. No. 4,409,927 to Loesch et al., incorporated herein by reference. Although the present invention described hereinbelow can be used for the various oil or gas well applications requiring nitrogen gas, one particular application is on a barge from which a nitrogen stimulation job is to be performed at an offshore well.
It is known that during at least one type of an offshore nitrogen stimulation job, liquid nitrogen is pumped through a stainless steel manifolding to a sea water vaporizer in which the liquid nitrogen is heated and vaporized. Stainless steel manifolding at the outlet of the vaporizer connects to iron manifolding that conducts the vaporized nitrogen off the barge to the well or another vessel (e.g., a foaming vessel where the vaporized nitrogen is used to generate a foamed gel that is pumped into the well).
It is important to monitor the temperature at the stainless steel/iron manifolding joint to ensure that freezing temperatures are not present. The liquid nitrogen is stored at a very low temperature, such as -320.degree. F., so that significant heating must occur for the vaporized nitrogen to be formed and brought to ambient or near ambient temperature. If the vaporized nitrogen is not heated to above a freezing temperature, the manifolding can become clogged by ice plugs. This presents a dangerous situation if the vaporized nitrogen continues to be produced because this can increase the pressure sufficiently whereby the manifolding explodes.
In an attempt to prevent such a dangerous situation arising, a temperature gauge has been placed near the manifolding junction so that an operator can locally read the temperature. If the temperature gets below a predetermined level, the operator stops the pumping by manually shifting into neutral a transmission that couples a drive motor to the liquid nitrogen pump. Although this can prevent an overpressurization of the type described above, it still presents a potentially hazardous situation because the operator is located at the situs of the nitrogen pumping and vaporizing equipment, which is typically carried forward on the barge.
To avoid this latter potentially hazardous situation where a person has to be located at the nitrogen pumping and vaporizing equipment, there is the need for a remote monitoring and controlling capability. This preferably should occur in an automated manner so that a person does not need to continually watch one or more gauges or manually operate the equipment.